1. Field of the Invention
The present invention relates to a sealing device sealing between two members which are concentrically arranged and move relatively, and more particularly to a structure in which a main sealing body is installed together with a backup ring within an installing groove of one member, and the main sealing body is supported by the backup ring.
2. Description of the Conventional Art
Conventionally, as a sealing device which is used in equipment generating high fluid pressure to be sealed, for example, a hydraulic cylinder, a hydraulic shock absorber, a plunger type pump or the like, a structure as shown in FIG. 5 has been known.
In particular, a sealing device 100 shown in FIG. 5 is structured such as to seal working fluid within a sealing space S1 between an outer peripheral member 110 (for example, a cylinder of a hydraulic device) and an outer peripheral surface of an inner peripheral member 120 (for example, a piston of a hydraulic device) arranged in an inner periphery thereof so as to freely reciprocate in an axial direction, is constructed by a main sealing body 101 which is formed by a rubber-like elastic material (a rubber material or a synthetic resin material having a rubber-like elasticity), and a backup ring 102 which is arranged at the non-sealing space S2 side of the main sealing body 101 (at the side of a space opposite to the sealing space S1 as seen from the main sealing body 101), and is installed in a state of being contained within an installing groove 121 which is formed in an outer peripheral surface of the inner peripheral member 120. The main sealing body 101 is a so-called O-ring having a circular cross section, and is installed in an appropriately compressed state, between a bottom surface 121a of the installing groove 121 and an inner peripheral surface of the outer peripheral member 110.
In this case, the backup ring 102 is formed by a synthetic resin material which is harder than the main sealing body 101, and is structured such as to support the main sealing body 101 from the non-sealing space S2 side within the installing groove 121, for preventing the main sealing body 101 to which high pressure is applied at a time when the sealing space S1 comes to have the high pressure, from running over to a gap G1 between a groove shoulder at the non-sealing space S2 side in the installing groove 121 and the inner peripheral surface of the outer peripheral member 110 so as to be broken.
However, in accordance with the sealing device 100 provided with the structure mentioned above, a gap G2 between the backup ring 102 and the outer peripheral member 110 becomes larger in some instances due to a dimensional tolerance of the installing groove 121 or the backup ring 102, and even though the backup ring 102 is provided actually for closing the gap G1 between the outer peripheral member 110 and the inner peripheral member 120, there is a risk that the main sealing body 101 runs over to the gap G2 between the backup ring 102 and the outer peripheral member 110 so as to be broken, as shown in FIG. 6.
Accordingly, as a technique for preventing the gap G2 between the backup ring 102 and the outer peripheral member 110 as mentioned above from being made, for example, there has been known a technique disclosed in Japanese Unexamined Patent Publication No. 3-113179 and Japanese Unexamined Patent Publication No. 2009-8238.